This application is the US national stage of PCT/EP00/01383 filed Feb. 19, 2000 and is based upon German national application 19910832.3 filed Mar. 11 1999.
The invention relates to a method of drying veneers especially Messerfurnieren or sliced veneers as well as to a drying apparatus for carrying out the method.
It is generally used practice to the individual veneer sheets which are moist veneers as cut by the slicing machine, to a dryer to evaporate water to a predetermined residual moisture content and then to cool the veneers, to count them and to stack them. The veneers are so fed to the dryer that the fiber direction of the veneer is approximately at a right angle to the transport direction.
A feed device and a discharge device, each having a respective suction box are known from DE 25 23 482 A1. The applicant is also aware of a feed device which is a combination of suction boxes and a transport system equipped with belts and of a discharge device with a transport system having belts.
By the term xe2x80x9cdryer,xe2x80x9d for the purposes of the description to follow, a so-called sheet dryer is to be understood. With such a system two transport beltsxe2x80x94a support belt and a cover beltxe2x80x94are provided which lie directly parallel one above the other and between which the veneer is transported through the dryer with at least the not insignificant part of the transport path having multiple rerouting so that the veneer is alternately bent upwardly downwardly. The rerouting can be achieved in this case in various ways. Alternatively, pressure is applied by rollers on the upper transport belt.
In EP 0 152 576 B2, a dryer of this type is described in which the belt travel after a straight segment has loops around rollers with relatively large diameters, whereby a short linear segment is formed between two neighboring rollers.
EP 0 290 056 A2 describes a dryer of the type described with a sine-wave-shaped belt path which is achieved by many rollers of small diameter. Additional rod-shaped rollers can be used as well.
In DE 41 09 298 C2, a flattened omega configuration with a corresponding linear path is described for the transport belts in which there are a plurality of rollers forming the guide paths with at least the second and fourth rollers in the direction of the dryer inlet being spaced from the first and third rollers whereby the second and third rollers lie in a plane above the plane of the first and fourth rollers and the spacing of the two planes is less than the diameter of a roller.
DE 42 17 493 A1 described a zigzag belt travel which is achieved by offset rerouting rollers lying one above another.
In the dryer described in DE 37 06 353, the travel direction of the transport belts is approximately rectilinear. With the aid of vertically pressing rollers, which are offset in the transport direction and are arranged parallel to the support rollers, a sufficient pressure is generated on the veneer.
In the cooler, the transport belts are guided similarly to their pattern in the dryer.
The purpose of a sheet dryer is to smooth out corrugations in the veneer during the drying and cooling period. By comparison to dryers and coolers with straight belt paths and without the effect of pressure, a significantly better smoothing is obtained with most types of wood. However, with sensitive kinds of wood like, for example, beech, walnut and cherry wood, folds and cracks can arise which can make the veneer at least partly unusable. The waste can amount of 10 to 20%.
It is an object to provide a method for the drying of veneers which is applicable also for difficult to dry wood types and by means of which an unobjectionably smooth veneer can be obtained and in which the waste as a result of folds and cracks is minimized.
A further object is to provide a drying apparatus for carrying out the method according to the invention.
The first object is achieved with a method of drying veneers, especially sliced veneers, with at least the method steps of feeding, drying, optionally cooling and discharging the veneer, whereby the veneer during drying and optionally during cooling is rerouted a multiplicity of times between two transport belts and/or is exposed to pressure. According to the invention the veneer is given an inclined orientation during the feeding whereby the angle between the fiber direction of the veneer and a line perpendicular to the transport direction of the dryer amounts to 20xc2x0 to 60xc2x0, and that the veneer is dried and cooled in this inclined orientation.
Preferably the veneer upon discharge is brought from an inclined orientation into an orientation approximately at a right angle to the transport direction.
The veneer during the feeding and optionally during the discharge, as seen in the transport direction is transported with different speeds at the left and the right.
Because of the inclined orientation of the veneer in the dryer and in the cooler, a component of the crimping action tends to be applied in the fiber direction at the rerouting location. It has been found that all dried veneer leaves the dryer in this case without folds or cracks when the fiber direction of the veneer during the transport through the dryer and the cooler is inclined to the transport direction rather than as heretofore customary at right angles thereto.
Claims 2 and 3 facilitate the manual effort to service personnel.
The dependent claims 5 to 10 contain the preferred embodiments of a drawing device according to the invention. The features ensure a reliable operation of the drying device.
The inclined orientation, that is the angle between the fiber direction of the veneer and a line at a right angle to the transport direction, is provided by the insertion of the veneer into the dryer at a predetermined angle of 20xc2x0 to 60xc2x0 and preferably 30xc2x0 to 50xc2x0.
In the feed direction, the speeds of the veneer in the transport direction to the right and left are set differently so that the transfer of the veneer onto the support belt, that is the lower transport belt of the dryer, assumes the correct inclined position. During the drying and the cooling, the veneer is fixed in this position because it is mechanically held between the transport belts. The discharge device largely cancels the inclined position because of different speeds which correspond to the inverse of those in the feed device to facilitate further handling. The service personnel thus need not become accommodated to a different discharge or handling.
A preferred embodiment is the use of different diameters of the driven belt disks.
The use of individually driven belts enables a very flexible manner of travel and matching of the inclined orientation during the operation.
The brake device can be retrofitted to existing apparatus in a simple manner. Claims 9 and 10 indicate preferred embodiments of the brake device.